Conventional regeneration or power generation systems are a fueled power generation facility, a solar heat power generation facility or a wind power facility, etc. and have mainly been installed on the ground, which is very costly. Accordingly, due to this problem, they had much difficulties in being widely used as an urban power generation plant. Thus, recently the inventors began to review the method of using a power generation system for generating electric power by utilizing water, as an urban power generation plant.
The sewerage system is a generic term for conduits installed to collect and process home foul water, industrial water waste, rain and underground water, etc., discharged from various areas, and for other structures and facilities. Recently water storage facilities for storing water underground are being used in such sewerage system in order to prevent flood damage due to rain, etc., and to prevent temporal overflow of the river in case heavy rain falls intensively.
Example of these water storage facilities is disclosed in Japanese patent application publication No. 2000-352080. Example of a unit member of Japanese patent application publication No. 2000-352080 is illustrated in FIG. 1. The unit member (A), as shown in FIG. 1, includes a base portion 110 of a rectangular shape and a container portion 120 arranged such that it is integrally projected from the base portion 110. In addition, the unit member (A) has four container portions 120 formed symmetrically relative to a center. Example showing the configuration in which such unit members (A) are assembled in the top and bottom manner is illustrated in FIG. 2.
However, in case a water storage tank is configured by utilizing such unit member (A) only, the water storage tank is likely to collapse due to the load of soil, etc., and an installation space for generating electricity cannot be secured.